Asymmetric bilateral optic neuritis as the first presenting feature secondary to undiagnosed vitamin-B12 deficiency

Vitamin b12 deficiency (VBD) rarely cause involvement of optic nerve. Moreover, optic atrophy has been reported more commonly than optic neuritis secondary to VBD. Here, we report a 31-years old male presenting with bilateral but asymmetrical optic neuritis as the first clinical presentation secondary to undiagnosed VBD and showed drastic improvement in the vision after replacement with parenteral followed by oral Vitamin-B12. Thus, patients with ocular manifestations should be screened for VBD as well, particularly in the vegans. Though, VBD rarely cause optic neuritis, it should still be considered as one of the differentials; early diagnosis of which may prevent ocular morbidity.